There has been known heretofore a pipe coupling comprising female and male coupling members threadedly connected to each other (see Japanese Utility Model Public Disclosure Sho No. 60-127185). Such a pipe coupling is of simple structure and is easy to manufacture but it is difficult to use the coupling in a narrow space because the operation of connection of the female and male coupling members to each other cannot be easily performed.
There has also been known a steel ball type of pipe coupling in which a female coupling member is provided with a plurality of tapered holes formed at the inner periphery of a connector portion thereof for receiving steel balls and a male coupling member is provided with a groove formed therein for receiving the balls projected from their retracted position in the holes when the male coupling member is inserted into the connector portion of the female coupling member. A special machine is required to machine the tapered holes in the female coupling member and this will make the coupling more expensive. In addition, the groove in the male coupling member is liable to be deformed due to excessive local stress resulting from point-contacts between the steel balls and the groove. This results in a short life of the pipe coupling.